Currently, a large number of mobile terminals, such as mobile phones, tablets, or notebook computers, to which power is supplied by using batteries are applied in daily life of people. Charging and discharging control is generally performed on these devices by using a power path management architecture. As shown in FIG. 1, an existing charging apparatus includes a voltage regulator 1, a charging power tube M1, and a charging controller 2, where the voltage regulator 1 is configured to convert an input voltage Vin into an output voltage Vout, and the output voltage Vout generates, while supplying power to a load, a charging current Ichg by using the charging power tube M1, to charge a battery bat. As shown in FIG. 2, in order to increase charging efficiency, in an existing charging process, a fixed dropout is always maintained between an output voltage and a battery voltage, and Vov=Vout−Vbat, where Vbat is the battery voltage, Vov is a dropout between the output voltage Vout and the battery voltage Vbat, and a horizontal coordinate is time t. In the prior art, generally Vov is set to a fixed value, for example, in a charging process, Vov is maintained to be 200 mV; and in the charging process, Vout rises as Vbat rises. In this way, when the battery voltage is relatively low, relatively high charging efficiency can also be maintained. A minimum dropout between the output voltage Vout and the battery voltage Vbat is Vov−min=Rm1×Ichg, where Rm1 is conductive impedance of the charging power tube M1. The highest charging efficiency can be ensured only when Vov=Vov−min, that is, the dropout between the output voltage Vout and the battery voltage Vbat is maintained to be a minimum value. However, due to requirements of different application scenarios, usually the charging current Ichg is not a fixed value, and can be adjusted according to a register or an external resistor. Therefore, when Vov is set to a fixed value, relatively high charging efficiency cannot be maintained when a charging current changes.